The present invention relates generally to gas inflators for automotive passenger restraint systems, and more specifically, to an inflator having an improved restraint performance, a reduction in toxic gases, and an improved airbag release.
The composition of the gas stream emanating from an automobile airbag inflator is subject to strict requirements to avoid toxicity concerns. Generally, gas generators containing solid propellants produce unacceptable byproducts that must be removed from the gas stream prior to exiting the gas generator. Due to the high combustion temperatures of solid propellants, many of the unacceptable byproducts are in the form of liquids or gases. Liquids and gases are difficult to remove unless cooled to form filterable solids upon contact with the relatively cooler surfaces of the gas generator.
The conventional approach to solving the aforesaid problem has been to direct the hot propellant gases directly into a coolant/filter mass and rapidly cool the gases down in a single step to the point where the undesirable solid liquid byproducts are removed. However, a problem is presented by this approach in that rapid cooling of the gases may stabilize the gas combustion equilibrium in a manner that leads to unacceptably high levels of undesired gases.
For example, in airbag inflators, low levels of NO (nitrogen monoxide) and CO (carbon monoxide) in the effluent gases are mandated. When a stoichiometric propellant containing N, C and O is burned, the quantity of NO and CO produced is a function of the propellant combustion temperature. More CO and NO is formed at higher temperatures. If, as in a conventional system, the combustion gases are quenched in a single step to a temperature at which the gas reaction rates are reduced to essentially zero, incomplete combustion often results. Accordingly, correspondingly unacceptable high CO and NO levels may result given the combustion temperature equilibrium condition of these gaseous species.
As a solution to the problems described, multistage cooling filters have been designed. However, inefficient heat transfer and filter clogging are concerns still driving improvements in filter design.
Yet another problem involves the release of the airbag once the gas exits the inflator and begins to fill the airbag. The airbag must be timely released to ensure adequate occupant protection. At times, the airbag may not fully inflate resulting in less than optimum protection of the occupant. Therefore, an inflator incorporating a module opening aid would be an improvement in the art.
The aforesaid problems are solved, in accordance with a preferred embodiment of the present invention, by a gas generator or airbag inflator comprising a plurality of beads containing gel and water disposed around a propellant chamber of a conventional gas inflator. The plurality of beads operates, in conjunction with a primary expanded metal filter, as a secondary filter and heat sink, and, as an airbag release agent. By cooling the propellant combustion gases in stages and providing sufficient residence time within the generator, the CO and NO equilibrium conditions are shifted to relatively low, acceptable, CO and NO concentrations. At the same time, humidification or introduction of water vapor (released from the gelatin/water matrix) to substantially filtered combustion products reduces the pressure required to release and inflate an airbag in fluid communication with the inflator.